Acoustic wave detection probes have been conventionally used, for example, in ultrasonic imaging devices and photoacoustic imaging devices used for diagnosis, fish finders used in fishery, and the like. Such probes have acoustic lenses incorporated therein for focusing acoustic wave beams to improve resolution.
For example, Japanese Unexamined Patent Publication No. 2005-125071 discloses that the acoustic lens preferably satisfies mainly six characteristics in order to improve contact with a living body. The six specific requirements are: (1) to minimize reflection of ultrasonic waves at a contact portion with a measurement target; (2) to transmit and receive ultrasonic waves with high sensitivity; (3) to be made of a material whose acoustic velocity within the acoustic lens is equal to that within a measurement target (about 1500 m/s) or less so as to have a convex shape; (4) to be made of a material having excellent formability with, in particular, a large tearing strength; (5) constituent material thereof, including an additive, is harmless to living body; and (6) to be made of a material having hardness of a degree that may prevent easy deformation when used.
In order to provide an acoustic lens that satisfy all of the six requirements described above, Japanese Unexamined Patent Publication No. 2005-125071 discloses a composition obtained by mixing a predetermined mass concentration of zinc oxide powder or platinum powder in silicone rubber.
In relation to this, Japanese Unexamined Patent Publication No. 58 (1983)-216294 discloses an acoustic lens obtained by mixing titanium particles with a particle size of 0.08 to 0.20 μm in silicone rubber.